1. Field of the Invention
The present invention relates to magnetic resonance (MR) technology and, particularly to a method and an apparatus for implementing fat-water separation in an MR system.
2. Description of the Prior Art
The Dixon method has been used widely for a long time to separate MR signals respectively originating from fat and water, due to its relatively good fat-water separation function.
The three-point Dixon method is an improvement to the basic Dixon method, and in this method, the normally adopted mode of collecting the echo signals is out-of-phase—in-phase—out-of-phase, so as to acquire two out-of-phase images and one in-phase image, and phase differences caused by the inhomogeneity of a magnetic field are calculated on the basis of the two out-of-phase images, to implement the phase correction of in the two out-of-phase images, and finally they are combined with the in-phase image to produce the water and fat images.
In the three-point Dixon method, the time interval between two echo signals is very small, for example, for a 1.5 T MR system, the time interval between two echo signals is only 2.38 ms, and this puts a very high requirement to the gradient performance of the MR system. Normally, the bipolar gradient can substantially meet the requirement. As shown in FIGS. 1 and 2, FIGS. 1 and 2 are a water image and a fat image respectively which are produced by using the currently available three-point Dixon method to carry out the water-fat separation.